In a piezoelectric-driven diaphragm pump in which a piezoelectric element is used as an actuator, a diaphragm is driven by the piezoelectric element, and a capacity of a pump room is varied corresponding to the displacement of the diaphragm. When the capacity of the pump room is increased, a discharge valve is closed and a suction valve is opened so that a fluid is sucked into the pump room. Alternatively, when the capacity of the pump room is decreased, the suction valve is closed and the discharge valve is opened so that the fluid is discharged from the pump room. The diaphragm is driven by expansion and contraction of the piezoelectric element when an alternating voltage is applied between electrodes of the piezoelectric element. In such piezoelectric-driven diaphragm pump, a minute transformation of the piezoelectric element in a radial direction can be transformed to a large displacement in a thickness direction, so that the piezoelectric element can be driven by a low voltage. A power generated by the diaphragm, however, becomes lower because of using such a displacement enlarging mechanism.
On the other hand, a pump which discharges a fluid generally has a problem of internal contamination with the fluid. For example, when a fluid such as alcohol including solid matter is stayed in the pump, each component of the fluid or inclusion adheres on or dissolves the elements of the pump such as valves or pipes. As a result, the valves may be deteriorated so that the valves cannot be opened and closed normally. A life time of the pump may be shortened.
A method for solving the shortening of the file time of the pump, it is proposed to replace a portion of the pump where the fluid flows. Japanese Laid-Open Patent Publication No. 1-285681 discloses a conventional pump that a driving unit having a piezoelectric element and a valve unit having an inlet with a suction valve and an outlet with a discharge valve are detachably divided. When contamination or deterioration of the valves due to the fluid occurs, the valve unit can be replaced. The driving unit and the valve unit are coupled by screw-in fitting, and a tubular is fluid-tightly sealed by an elastic film. Although the elastic film must be compressed to a support member of a bimorph, when the elastic film is compressed to the support member with a strong force, it disturbs vibration of the bimorph.
Official Gazette of Japanese Utility Model Registration No. 2542620 discloses another conventional pump comprised of an actuator unit and a pump unit detachably coupled to the actuator unit, thereby only the pump unit can be replaced. Since the actuator unit and the pump unit are coupled by a double-sided adhesive tape or a hook and loop fastener, a piezoelectric diaphragm may be damaged at the replacement of the pump unit.
Japanese Laid-Open Patent Publication No. 6-24492 discloses still another conventional pump that a driving object having a piezoelectric element as an actuator is detachable from a main pump unit, and the driving object applied a displacement to a side wall of the main pump unit made of a flexible material. However, the displacement of the piezoelectric element in a direction perpendicular to the side wall is smaller, and the displacement transmitted member has a flat shape, so that the transmission efficiency of the displacement of the piezoelectric element is lower. Further more, it needs a coupling member such as a double-sided adhesive tape for coupling the driving object to the main pump unit.
Japanese Laid-Open Patent Publication No. 2004-353493 discloses still another conventional pump that a space between a driving diaphragm and a driven diaphragm is sealed, and vibration of the driving diaphragm is transmitted to the driven diaphragm by a transmission medium filled in the sealed space.
FIG. 28 shows the conventional piezoelectric-driven diaphragm pump disclosed in Japanese Laid-Open Patent Publication No. 2004-353493. The conventional piezoelectric-driven diaphragm pump 200 is comprised of a driving unit having 201a driving diaphragm 203 driven by a piezoelectric element 202, a replaceable driven unit 204 and a fixing unit 209 for fixing the driven unit 204 to the driving unit 201. A transmission medium 210 such as a liquid is filled in a sealed space 211 between the driving diaphragm 203 of the driving unit 201 and a driven diaphragm (driven film) 205 of the driven unit 204 so as to transmit the vibration efficiently. Thereby, the vibration of the driving diaphragm 203 can be transmitted to the driven diaphragm 205 via the transmission medium 210, and thereby, the driven unit 204 can perform a pump motion. Specifically, alternative of the valves 207 is opened and the rest is closed by variation of a capacity of a pump room 206 of the driven unit 204, so that a fluid in the pipe 208 is sucked into the pump room 206 and a fluid in the pump room 206 is discharged to the pipe 208.
In the conventional piezoelectric-driven diaphragm pump 200, the driven diaphragm 205 is formed in a flat plate shape, and the driven diaphragm 205 is not contact with any portion of the driving diaphragm 203. When the driving diaphragm 203 is displaced so as to reduce a capacity of the sealed space 211, the driving diaphragm 203 presses the transmission medium 210 and the pressed transmission medium 210 further pressed the driven diaphragm 205. Thereby, the driven diaphragm 205 is driven for decreasing the capacity of the pump room 206. Alternatively, when the driving diaphragm 203 is displaced so as to reduce a capacity of the sealed space 211, a pressure of the transmission medium 210 is reduced so that a negative pressure occurs in the sealed space 211. Thereby, the driven diaphragm 205 is driven for increasing the capacity of the pump room 206.
The above-mentioned conventional piezoelectric-driven diaphragm pump 200 has a problem that a volume of the transmission medium 210 is varied corresponding to the pressure, so that the vibration of the driving diaphragm 203 cannot be transmitted to the driven diaphragm 205 directly. Especially, when a frequency of the vibration of the driving diaphragm 203 is lower, following performance of the driven member 205 is splendid. However, when the frequency of the vibration of the driving diaphragm 203 becomes higher, the following performance of the driven member 205 is lowered.
Furthermore, when the driven unit 204 is replaced, it is difficult to fill the transmission medium all 210 such as a liquid into the sealed space 211 without containing air chambers. If the air chambers are contained in the transmission medium 210, transmission efficiency of the transmission medium 210 for transmitting the vibration of the driving diaphragm 203 to the driven diaphragm 205 may be lowered.